Control Broods Research Articles

Opposing selective pressures on hatching asynchrony: egg viability, brood reduction, and nestling growth

At least 19 hypotheses have been proposed to explain the evolutionary significance of avian hatching asynchrony, and hatching patterns have been suggested to be the result of several simultaneous selective pressures. Hatching asynchrony was experimentally modified in the black kite Milvus migrans by manipulating the onset of incubation during the laying period. Delayed onset of incubation reduced egg viability of first-laid eggs, especially when ambient temperature during the laying period was high. Brood reduction (nestling mortality by starvation or siblicide) was more commonly observed in asynchronous nests. The growth rate was slower in synchronous broods, probably due to stronger sibling rivalry in broods with high size symmetry. Last-hatched chicks in synchronous broods fledged at a small size/mass, while in control broods, hatching order affected growth rates, but not final size. Brood reduction, variable growth rates, and the ability to face long periods of food scarcity are probably mechanisms to adjust productivity to stochastic food availability in a highly opportunistic predator. The natural pattern of hatching asynchrony may be the consequence of opposing selective forces. Extreme hatching synchrony is associated with slow growth rates, small final size of last-hatched chicks, and low viability of first-laid eggs, while extreme hatching asynchrony is associated with high mortality rates. Females seem to facultatively manipulate the degree of hatching asynchrony according to those pressures, because hatching asynchrony of control clutches was positively correlated with temperature during laying, and negatively correlated with the rate of rabbit consumption.

Exposure to ectoparasites increases within-brood variability in size and body mass in the sand martin

Parasites often have detrimental effects on their hosts, and only host individuals able to cope with parasitism are likely to display induced or genetic resistance. Hosts may respond to parasitism by differential investment in offspring depending on their ability to cope with parasitism, because offspring that perform better than their siblings are themselves likely to have superior induced or genetic resistance. We tested whether nestlings of the highly colonial sand martin Riparia riparia were affected by the haematophagous tick Ixodes lividus by experimentally manipulating parasite loads of nests [nests sprayed with pyrethrum to remove parasites (sprayed), or nests sprayed with water (control)] at three stages of the breeding season. Prevalence and intensity of ticks were significantly affected by treatments. Breeding success was not significantly affected by treatment, although post-fledging survival was twice as high among nestlings from sprayed nests than from controls. Mean phenotypic traits of nestlings generally did not differ significantly among treatments, while within-brood variance in keel length (a skeletal character) and body mass were higher in control treatment broods than sprayed ones. Sedimentation rate, which reflects blood protein and immunoglobulin content, was significantly higher and less variable in sprayed than control broods. These findings are consistent with the suggestion that parasitism effects on host reproductive success act through an increase in the variance of offspring quality.

Food‐supplementation does not override the effect of egg mass on fitness‐related traits of nestling house wrens

1. Cross‐fostering experiments have shown that egg mass per se positively affects post‐hatching growth and development in passerine birds. In most studies, however, the initial influence of egg mass was not sustained, leading to questions about the importance of egg mass relative to the cumulative effects of environmental factors during the period of post‐hatching care. 2. In house wrens, Troglodytes aedon Vieillot, evidence from cross‐fostering experiments suggests that food availability mitigates the influence of egg mass on posthatching growth: early in the season, when food was putatively abundant, the initial effect of egg mass was lost as nestlings aged; however, later, when food was putatively scarcer, the effect of egg mass persisted until nestlings left the nest. 3. We tested the hypothesis that abundant food for provisioning nestlings can decouple the relationship between fitness‐related traits of nestlings and the mass of the eggs from which they hatch (‘egg‐mass override hypothesis’) by providing daily mealworm supplements to broods of house wrens. 4. The food supplements did not increase final nestling mass, final nestling tarsus length, growth rate, or survival until nest‐leaving in late‐season broods, when the hypothesis of food limitation predicts that there should be such an effect. Instead, the food supplements significantly, but only slightly, increased final nestling mass in early‐season broods, when food is putatively abundant. 5. The effect of the food supplements on final nestling mass was independent of egg mass. Nestling survival in early‐season broods, and final nestling mass and tarsus length in both early and late‐season broods significantly increased with increasing egg mass in both experimental and control broods. 6. We propose that food was not limiting during the course of the experiments and that final nestling mass and tarsus length remained positively related to egg mass because nestling growth and development in house wrens is ‘predetermined’ by some component or property of eggs that covaries with egg mass.

ESTABLISHMENT AND PERSISTENCE OF MASS HIERARCHIES IN BROODS OF THE BROWN PELICAN

I investigated the roles of intraclutch variation in egg volume and hatching asynchrony in the establishment of mass hierarchies in broods of the Brown Pelican (Pelecanus occidentalis). The second egg averaged 2.6% larger than the first and 1.9% larger than the third. In unmanipulated control broods, first eggs hatched an average of 25 h before second eggs, which hatched 40 h before third eggs. On the day the last egg hatched, first chicks averaged 16% heavier than second chicks and 30% heavier than third chicks. Although chick mass at hatching was strongly correlated with egg volume, differences in mass within broods were almost entirely the result of hatching asynchrony. In broods in which I experimentally reduced hatching intervals, initial nestling mass differences were significantly smaller and strongly correlated with differences in egg volume but not with hatching asynchrony. Intrabrood mass differences remained lower in experimental than control broods throughout the first 2 weeks of the nestling period. Furthermore, mass ranks established at hatching were less likely to persist through this period in experimentally synchronized broods than in asynchronous controls. These results indicate that hatching asynchrony promotes the establishment of a more stable size hierarchy. However, the adaptive significance of nestling size hierarchies in Brown Pelicans remains unresolved.

Risk-taking restraints in a bird with reduced egg-hatching success.

Risk taking, as is any other phenotypic and/or behavioural trait, is determined by proximate constraints related to time or resource availability and by evolutionary adaptive restraints related to the differences in the costs of risk taking and its benefits in terms of fitness. Because risk taking is influenced by many confounding variables related to experimental design, environment, parents and offspring, few field studies have been reported which unambiguously separate the effects of restraints from those of constraints. We compared parental risk taking in blue tits (Parus caeruleus) during brood defence towards a nest predator in broods with experimentally reduced and natural egg-hatching success leaving the original number of eggs in the nest. The experimentally reduced broods had more time or resources available and lower risk-taking benefits compared to the control broods. 'Constraint' would predict more risk taking in broods having experimentally reduced egg-hatching success, whereas 'restraint' would predict the opposite effect with more risk taking in broods with natural egg-hatching success. We report, to our knowledge, the first field study experimentally demonstrating a brood defence restraint in response to reduced egg-hatching success. This demonstration was only possible after controlling for more than 20 potential confounding variables showing once more how complicated it is to separate proximate from evolutionary levels of analyses in natural populations.

Sex ratio and fledging success of supplementary-fed Tengmalm's owl broods.

A nest box population of Tengmalm's owls (Aegolius funereus) in northern Sweden was studied to investigate the effects of extra food on the sex ratio between hatching and fledging in this sexually size-dimorphic species. The brood size and brood sex ratio of supplementary-fed and control broods were compared. Newly hatched nestlings were blood sampled and sexed by polymerase chain reaction (PCR) amplification of the sex-linked CHD1Z and CHD1W genes. The brood sex ratio at hatching was strongly male biased (65%); this was also the case in broods where all eggs hatched (72%). There was no relationship between hatch order and sex ratio, and hatching sex ratio did not vary significantly with laying date. Brood size decreased between hatching and fledging, but did not differ between fed and control broods at either stage. Brood sex ratio did not differ between hatching and fledging, and fledging sex ratio did not differ between fed and control broods. It was concluded that, at least during the year in which the study was carried out, feeding had no effect on brood reduction, and that male and female nestlings did not show any differential mortality. The mechanisms behind the male-biased sex ratio at hatching, and any possible adaptive reasons for it, are not known.

EVOLUTION OF CLUTCH SIZE IN THE EASTERN KINGBIRD: TESTS OF ALTERNATIVE HYPOTHESES

David Lack proposed that parental feeding ability ultimately limited clutch size in bird species in which the young were dependent upon their parents for food. However, many species can raise broods that are larger than their normal clutch size. Based on nine years of experimental results from an individually marked population of Eastern Kingbirds (Tyrannus tyrannus) breeding in central New York (USA), I test six hypotheses that have been proposed as explanations for why birds fail to lay larger, seemingly more productive clutch sizes. I modified brood sizes by adding or removing 1–2 nestlings when broods were 1–3 d old and then documented the effects of brood size and manipulated brood size on nestling size and survivorship, offspring recruitment, adult survival, and future adult reproduction. Most first clutches of the season held three eggs (62% of 503 clutches), but the proportion of young to fledge did not vary with brood size (1–5 young), and as a result, broods of five were the most productive. Lack's basic food-limitation model was thus rejected. Although nestling mass and ninth-primary length at fledging declined with brood size, offspring survival during the immediate 10–12 d period after fledging was unrelated to nestling mass or lengths of the tarsus or ninth primary. The findings that the underweight young in broods of four and five did not suffer disproportionate mortality and that they were just as likely to appear as recruits in future years led to a rejection of the extended version of Lack's food-limitation model. Comparisons of annual variation in the relationship between productivity and brood size showed that productivity increased with brood size in eight of nine years (significant in six years). Thus, high temporal stochastic variation in conditions for rearing young (the “bad-years” hypothesis) is unlikely to explain the relatively small clutch size of kingbirds. Predictions of two other hypotheses that predict asymmetrically low survivorship of young in large broods (the “cliff-edge” and “brood-parasitism” hypotheses) were also rejected. On the other hand, evidence suggested that females individualize clutch size such that each female lays a clutch that matches her individual feeding ability. Although fledgling production was not adversely affected by experimental increases in brood size, most enlarged broods lost young during the 10–12 d immediately after fledging. Thus, enlarged broods ultimately produced no more independent young than did control broods that began with the same number of eggs. Fledgling deaths were not related to nestling mass or size, and recruitment was independent of manipulations. Survival and fecundity costs of reproduction also existed for females. Male survival (68%) was independent of the number of young that had been raised (0–5 young), and future breeding efforts were not compromised by elevated effort in the past year. However, females that raised broods of five were less likely to return to breed in the following year (42%) than were females that raised 2–4 young (62%). Among the survivors, females that raised enlarged broods in the preceding year also experienced more hatching failure and fledged fewer young than females that raised reduced broods in the preceding year. I suggest that costs of reproduction probably set the ultimate limit to clutch size in Eastern Kingbirds. I did not test the hypothesis that high rates of nest predation favor the evolution of small clutch size, but given that predators destroyed ∼50% of nests each year, it is also likely that nest predation has contributed to the evolution of the current clutch size of kingbirds. Whether a female produces a clutch of three or four eggs is probably determined by individual differences in parental ability, which may be related to either intrinsic properties of the female or territory quality.

Testing the intergenerational conflict hypothesis: factors affecting adoptions in Audouin's gulls, Larus audouinii

We studied chick adoption in Audouin's gull, Larus audouinii, a ground-nesting seabird, to test several predictions made by the intergenerational-conflict hypothesis (ICH). The effects of food availability on adoptions were considered by comparing two breeding seasons with differing food supply. As predicted, adoptions were significantly more frequent when food was in shorter supply (48% of broods affected) than when it was more available (18.5%). Adoptions occurred during the first week of the chick-rearing stage; after that, aggression by adults towards intruding chicks increased significantly, which suggests that mechanisms of parent-offspring recognition were established. Foster parents incurred certain costs, since their offspring had lower chances of survival than those in control broods. However, contrary to the ICH hypothesis, adoptees did not select foster broods in relation to the age of the resident chicks. Survival of wandering chicks was no higher than that of chicks who stayed in their natal brood. Results suggest that chicks move only as a response to neighboring chicks being fed by an adult, and in Audouin's gulls, adoptions might be considered reproductive errors.

Chick Begging Strategies in Relation to Brood Hierarchies and Hatching Asynchrony.

Altricial offspring solicit food by begging, and their parents feed them according to begging intensity, which has been shown to be positively related to offspring need. Parent-offspring genetic conflict calls for analyses of evolutionary stability, and various theoretical models have shown that stability is possible in the framework of handicap theory. The models predict that a negative relationship exists between offspring condition and begging and that offspring in poorer condition should be fed preferentially. However, these predictions depend on two unsatisfactory assumptions. First, they assume a monotonically decelerated relation between condition and fitness (this function is more likely to be sigmoid); second, they ignore physical competition between siblings, which is known to be important. We examined the significance of these issues by manipulating hatching asynchrony in broods of starlings Sturnus vulgaris, thus controlling competitive asymmetries between nest mates. We created broods with senior (older) and junior (younger) chicks and control broods with synchronous chicks. In field and laboratory experiments, we found that seniors begged less than juniors and controls, whereas juniors did not differ significantly from controls. However, seniors received more food from their parents and grew better than juniors or controls (hence, they were in better condition). These results violate the predictions of available theoretical models and, together with limitations in the universality of their assumptions, indicate that fundamental aspects of parent-offspring communication are not yet understood.

Brood desertion in Kentish plover: the value of parental care

To understand the evolution of parental care, one needs to estimate the payoffs from providing care for the offspring and from terminating care and deserting them. In this study we estimated the payoff from care provision, and in a companion paper we analyze the payoff from offspring desertion. In the current study we experimentally investigated the influence of the number and sex of attending parents on growth and survival of offspring in the Kentish plover Charadrius alexandrinus, in two sites (A and B). Either the male or the female parent was removed from some broods at hatching of the chicks (female-only and maleonly broods, respectively), whereas in control broods both parents were allowed to attend their young. At site A survival of the chicks was lower in uniparental (male-only and female-only) broods than in control broods, whereas we found no difference in brood survival at site B. Brood survival decreased over the season. Removal of either parent did not influence the growth of the young, although growth varied over the breeding season, and it was significantly different between the sites. These results suggest that the payoff from parental care decreases over the breeding season and that the value of parental care (i.e., the contribution of parents to the survival of their young) may depend on the environment. Key words: biparental care, Charadrius alexandrinus, Kentish plover, mate removal, offspring desertion, parental care, uniparental care. [Behav Ecol 10:191‐197 (1999)]

Sibling aggression, hatching asynchrony, and nestling mortality in the black kite ( Milvus migrans )

In siblicidal species, hatching asynchrony could act to reduce sibling rivalry or promote the death of last-hatched chicks. The pattern of hatching asynchrony was experimentally altered in the black kite Milvus migrans. Hatching asynchrony in control broods was intermediate between those of experimentally synchronised and asynchronised broods. Sibling aggression and wounds on the chicks were more commonly observed early in the nestling period and in synchronous nests. Serious injuries were observed on last-hatched chicks in asynchronous nests, as were observations of intimidated or crushed chicks. Sibling aggression was related to food abundance, but some chicks died at an early age in nests with abundant food (cainism). Cainism was more commonly found in asynchronous nests. For species with facultative siblicide, moderate hatching asynchrony could be a compromise between reducing sibling rivalry and avoiding large size differences between sibs that would result in cainism. Female black kites preferentially fed the smallest chicks and exhibited behaviours to reduce sibling aggression, contrary to observations in other siblicidal species. In a highly opportunistic forager such as the black kite, a strategy may exist to protract the life of all the chicks in the brood, waiting for unpredictable situations of food overabundance. This would induce the appearance of a parent-offspring conflict over brood reduction, reflected in the existence of a possible anticipated response by some of the chicks (cainism) and in the appearance of special behaviours by the parents to selectively feed smaller chicks or reduce sibling aggression. In this facultatively siblicidal species, cainism does not seem to be the final stage of an evolutionary trend favouring the raising of high-quality chicks, but a manifestation of a parent-offspring conflict over brood size.

The effect of experimental male removals on extrapair paternity in the wheatear,Oenanthe oenanthe

To examine the role of the pair male in ensuring paternity in the wheatear, we removed pair males for 24h during the fertile period (days 0 to +1 in 1992 and days −5 to −1 in 1993, where day 0=first egg date). Control males were removed during incubation. The frequency and duration of intrusions, and the frequency of extrapair copulations (EPCs), increased during removals in the fertile period, but not during incubation. The frequency of extrapair paternity (EPP) was marginally higher (25%) in experimental than control broods and the presence of the pair male seemed particularly important in ensuring paternity in those days immediately preceding laying. Females were selective over which males they copulated with in the absence of their mate and rejected the majority of attempted EPCs. Only extrapair males in better body condition than the removed pair male eventually gained successful matings. Experimental males in poorer body condition were also more likely to have EPP in their brood than experimental males in better body condition. Female copulatory behaviour was the most important factor in determining patterns of paternity, and mate-guarding behaviours by the pair male appeared to limit the females’ opportunities to engage in EPCs by reducing the frequency and duration of intrusions, rather than to control female behaviour directly.

The price of eggs: increased investment in egg production reduces the offspring rearing capacity of parents

Understanding the selective pressures shaping the number of offspring per breeding event is a key area in the study of life-history strategies. However, in species with parental care, costs incurred in offspring production, rather than rearing, have been largely ignored in both theoretical and empirical studies until relatively recently. Furthermore, the few experimental studies that have manipulated production costs have not yet teased apart effects that operate via the parental phenotype from effects on the quality of the resulting young. To examine whether increased egg production influences parental brood rearing capacity independently of effects operating via egg quality, we experimentally increased egg production in gulls and then examined their capacity to rear a control clutch. We found that the capacity of parents to rear the control brood was substantially reduced solely as a consequence of having themselves produced one extra egg. The paradox that, in many species, parents apparently aim for fewer young per breeding event than the experimentally and theoretically demonstrated optimum, has partly arisen from the failure to take into account the constraints imposed by production costs.

Does brood reduction provide nestling survivors with a food bonus?

Siblicide is common in many asynchronously hatching birds, including brown pelicans,Pelecanus occidentalisMost adaptive models of siblicide, and of brood reduction in general, tacitly assume that parental deliveries of food remain fixed, and therefore that supplies to seniors remain unchanged or increase after a junior’s death. If parents match deliveries to brood size, however, then seniors may get less food following brood reduction. To test the assumption that parental deliveries remain constant, and to determine how brood reduction affected seniors, food deliveries to control (three-chick) and experimentally reduced (two-chick) broods of brown pelicans were compared. Parents brought less food to reduced than to control broods. Similarly, a literature review revealed that avian parents generally delivered less food to smaller than to larger broods of experimentally altered sizes. In brown pelicans, when food deliveries decreased following brood reduction, second-hatched (‘B’) chicks received less food, but first-hatched (‘A’) chicks’ supplies remained unchanged. B-chicks may have gained more in control broods by appropriating the extra food that last-hatched (‘C’) chicks otherwise would have gained. If brood reduction decreases fighting, nestlings may gain more net energy even if they receive less food. Fighting did not decrease significantly in reduced broods, perhaps because fledging averaged one chick/brood, so A and B-chicks still competed intensely. Alternatively, small sample sizes may have prevented detection of differences in fighting. Seniors did not concentrate their attacks on C-chicks, perhaps because seniors may benefit by delaying the decreases in parental food deliveries that follow brood reduction.

Mass Loss in Breeding Blue Tits: The Role of Energetic Stress

1. The hypothesis that mass reduction in breeding passerines results from energetic stress was evaluated using data on body mass changes in female blue tits Parus caeruleus. 2. In accordance with both the adaptive adjustment and the physiological stress hypotheses, females with experimentally enlarged broods lost more mass than females rearing reduced or control broods. However, the ability to allocate energy to self-maintenance (as measured by the regrowth rate of a tail feather removed during incubation) was negatively correlated with the amount of lost body mass. 3. In one of the study years, loss of body mass was more pronounced among small females, suggesting that larger females are better able to cope with poor food conditions during breeding. 4. In a poor-weather year, 30% of the females deserted their clutches, compared with 8% in a good year. Females that deserted their clutches before hatching were significantly lighter during incubation than non-deserters, indicating that good body condition is important for successful reproduction. 5. In one year young females lost more mass than older females and therefore the ability to maintain adequate body condition in the face of energetic stress appears to be age-dependent. 6. Taken together, these results suggest that mass loss in breeding blue tits is, to some degree, attributable to energetic stress, although we have not ruled out the possibility that flight cost reductions may help explain the phenomenon.

Reproductive investment and parasite susceptibility in the Great Tit

1. Reproduction and parasite defence are assumed to be costly activities for hosts, and therefore trade‐offs might exist between reproduction and parasite defence. 2. Brood sizes were manipulated in a population of Great Tits (Parus major L.) to assess trade‐offs between reproduction and parasite defence. Blood samples were taken from males and females during the late nestling phase, and parasite prevalence was compared among parents raising enlarged, reduced and control broods. 3. A higher prevalence of protozoan blood parasites dominated by Haemoproteus majoris was found among parents with enlarged broods, as compared with parents with control and reduced broods, respectively. Brood size manipulation did not affect parasite prevalence between the sexes or between age classes differently. 4. Mean parasite intensity (number of parasites per microscope field) among adult birds only infected with H. majoris was higher for parents with experimentally enlarged broods than controls and reduced broods, respectively. 5. These results support the hypothesis of a trade‐off between parasite defence and reproduction.

Brood size manipulation in mallard ducks: Effects on duckling survival and brooding efficiency

:Parental care occurring after hatching of eggs in precocial birds has been assumed to have no effect on offspring survival because young feed themselves, and behaviour such as vigilance or defence benefits all young regardless of brood size. We tested this assumption by manipulating clutch and brood size of wild mallards (Anas platyrhynchos) and subsequently monitoring survival of ducklings. Offspring survival in enlarged broods tended to be lower than in control broods. By 14 days after hatching, enlarged broods had no more ducklings surviving than did controls. Brooding efficiency (i.e., the effectiveness of heat transfer from a care-giving female to her young) was evaluated with captive mallards in an environmental chamber where we manipulated ambient temperature and brood size, and monitored duckling temperature (Td). There was no difference in Td in broods of different sizes, but variation in Td increased with brood size. Under natural conditions, the female’s inability to effectively cover large broods could reduce duckling survival. Thus, brooding may represent one post-hatching behaviour that could limit clutch size in precocial birds. This study provides new insights regarding the implications of brood size on the survival of precocial young.

Brood size manipulations within the natural range did not reveal intragenerational cost of reproduction in the Willow TitParus montanus

To test for the existence of a reproductive cost, we manipulated brood sizes (‐2 and +2 nestlings) over 6 years in a northern population of Willow TitsParus montanusbreeding in natural holes. Possible effects were sought in subsequent survival and fecundity of the parents. Parents given extra chicks made more feeding visits than did parents with reduced and control broods. However, this was not reflected in differences in parental body‐weight between groups at the end of the nestling period. Brood size manipulation did not significantly affect female or male survival. In 4 out of 6 years, there was a weak and nonsignificant effect on male survival, consistent with a cost of reproduction. Female and male fecundity in the year following the experiment was not affected by the manipulations. Thus, the data do not give evidence of an intragenerational cost of reproduction in the Willow Tit. Parents appeared unwilling to increase their breeding effort to a level which jeopardized their own survival or future breeding success. It is possible that, because of the time constraints in northern latitudes, females work under their capacity and lay smaller clutches than would otherwise be most profitable. Thus, no costs to the parents would be expected as a consequence of manipulations. These results suggest that the current reproductive rate is not maintained by reproductive cost in the Willow Tit. However, the results do not rule out the possibility that selection has operated outside the current range of reproductive rates during evolutionary history of the species.

Patterns of Per-Brood and Per-Offspring Provisioning Efforts in the Willow Tit Parus montanus

Nestling feeding behaviour of Willow Tits Parus montanus was studied in natural and artificially size-altered broods at Oulu, northern Finland. Per-brood provisioning effort was positively and per-offspring effort negatively correlated with brood size. Brood size manipulations (about + 30% relative to control broods) did not significantly affect the patterns of per-offspring provisioning effort, i.e. parents of enlarged broods could increase their per-brood effort significantly as compared with control broods. Thus, Nur's refined trade-off model of optimal nestling feeding was supported. On the other hand, no measurable extra costs (in physical condition, body mass or size) to parents of enlarged broods were detected; however, the young of enlarged broods had lower body masses than those of control and reduced broods confirming earlier results in the same population. Thus, in broods above the modal size parents primarily tried to ensure their own rather than their offspring's survival. At the beginning of the nestling period, when females brooded the young, male contribution to provisioning was higher. At the end of the nestling period male load sizes were larger but female visiting rates slightly higher, resulting in sexually equal total feeding effort. This was expected for a monogamous passerine with biparental care. Feeding effort increased with offspring age owing to the increased load sizes, increased female feeding rates and prolonged working days. However, the temporal increase in female visiting rates may be explained by the decreased brooding effort. A temporal increase in feeding effort is consistent with the corresponding increase in nest defence intensity, found in our earlier studies.

Maternal Defence of a Leaf Beetle is not Effective against Parasitoids but is against Pedestrian Predators

AbstractFemales of the subsocial leaf beetle Gonioctena sibirica attend their broods on the willow Salix bakko. Females with broods settle on the underside of the basal part of leaves and face towards the base of the shoots. If other arthropods approach such attendant females, the females show aggressive behaviour against the intruder. The effectiveness of maternal care on offspring survival against pedestrian predators and against a parasitoid wasp was evaluated in field experiments using three groups: broods from which parent females were experimentally removed, those from which females were removed and pedestrian predators were excluded by tanglefoot treatments, and control broods. These experiments showed that maternal care was highly effective against pedestrian predators, but parasitism was not affected by the presence of females. Offspring mortality by predation or by parasitism was not usually dependent on larval densities. Position and orientation of attendant females will be effective for them to detect intruders which approach their larvae by walking along the stem, while it can inhibit the females from detecting parasitoids which fly and land directly on the leaf close to the larvae. The results suggest a trade‐off in the effectiveness of prey defensive behaviour against different enemy species: prey defensive behaviour specific to one type of the enemy may make the prey more vulnerable to the other.